In recent years, in the field of optical communications, the WDM(Wavelength Division Multiplexing) optical communications is vigorously researched and developed in order to increase transmission capacity, and is being practically used. In the optical wavelength division multiplexing communications, for example, plural lights having a wavelength different from one another are multiplexed in wavelength and are transmitted. The WDM optical communications system includes an optical transmitting device that transmits only the beams of light having predetermined wavelengths in order to extract the light beam of each wavelength from the multiplexed beams at a light receiving side.
FIG. 4 shows an arrayed waveguide grating (AWG) of a planar lightwave circuit by way of one example of the optical light transmitting device. In the arrayed waveguide grating, a waveguide is formed from quartz based glass on a substrate 11 of silicon etc. as shown in FIG. 4. This waveguide is composed of: one or more optical input waveguides 12 arranged side by side; a first slab waveguide 13 connected to the exit end of the optical input waveguide 12; An arrayed waveguide 14 connected to the exit end of the first slab waveguide 13; A second slab waveguide 15 connected to the exit end of the arrayed waveguide 14; and a plurality of optical output waveguides 16 arranged side by side and connected to the exit end of the second slab waveguide 15.
The arrayed waveguide 14 propagates light that is outputted from the first slab waveguide 13, and is composed of a plurality of channel waveguides 14a that are arranged side by side. Lengths of adjacent channel waveguides 14a are different from each other with the preset difference (xcex94L). For example, the optical output waveguides 16 are arranged in accordance with the number of signal lights having wavelengths different from each other and divided by the arrayed waveguide grating. Many channel waveguides 14a such as 100 channel waveguides are normally arranged. However, in FIG. 4, the numbers of optical output waveguides 16, channel waveguides 14a and optical input waveguides 12 are schematically shown for brevity of this figure.
For example, an optical fiber on a signal transmitting side is connected to the optical input waveguide 12, and wavelength multiple light is introduced into the optical input waveguide 12. Light having traveled through the optical input waveguide 12 introduced to the first slab waveguide 13 is diffracted by the diffraction effect and enters to the arrayed waveguide 14 to travel along the arrayed waveguide 14.
Having traveled through the arrayed waveguide 14, the light reaches the second slab waveguide 15, and is further converged into the optical output waveguide 16, and is outputted. However, since the setting amounts of lengths of the respective channel waveguides 14a of the arrayed waveguide 14 are different from each other, a phase shifts between the individual beams of light are occured after this light is propagated in the arrayed waveguide 14. A wave front of the beams of light is inclined in accordance with this phase shift, and a converging position is determined by an angle of this inclination. Therefore, the converging positions of lights having different wavelengths are different from each other. Thus, the lights having different wavelengths can be outputted from the different optical output waveguides 16 every wavelength by forming the optical output waveguides 16 in the respective converging positions.
For example, as shown in FIG. 4, when wavelength multiple lights of wavelengths xcex1, xcex2, xcex3, . . . , xcexn (n is an integer equal to or greater than 2) are inputted from one optical input waveguide 12, these lights are deffracted by the first slab waveguide 13, and reaches the arrayed waveguide 14. Then, these lights are converged in different positions in accordance with wavelengths through the second slab waveguide 15 as mentioned above, and are entered to the optical output waveguides 16 different from each other. These lights are outputted from the exit ends of the optical output waveguides 16 through the respective optical output waveguides 16. An optical fiber for optical output is connected to the exit end of each optical output waveguide 16, and the light of each wavelength is taken out through this optical fiber.
In this arrayed waveguide grating, waveguide resolution of the arrayed waveguide grating is proportional to the difference (xcex94L) in length between the adjacent channel waveguides 14a of the arrayed waveguide Therefore, wavelength multiple light having a narrow wavelength interval unable to be realized in the conventional multiplexer/demultiplexer can be multiplexed and demultiplexed by greatly setting the difference xcex94L in design. Thus, it is possible to fulfill a multiplexing/demultiplexing function of optical signals required to realize optical wavelength division multiplexing communications of high density, i.e., a function for demultiplexing/multiplexing a plurality of optical signals having a wavelength interval equal to or smaller than 1 nm.
The arrayed waveguide grating utilizes the reciprocity (reversibility) principle of an optical circuit. Therefore, the arrayed waveguide grating functions as an optical demultiplexer and also functions as an optical multiplexer. That is, in a direction reverse to the direction in FIG. 4, the light beams having a plurality of different wavelengths enter the optical output waveguides 16 corresponding to the respective wavelengths, then travel through the transmission path in the reverse direction. These light beams are multiplexed in the arrayed waveguide 14 and exit through one optical input waveguide 12.
The invention provides a manufacturing method of a metallic film to a planar lightwave circuit. This method comprises the following steps of:
preparing a mask having a hole approximately formed in the same shape as the metallic film manufactured on at least one of front and rear faces of the planar lightwave circuit;
arranging the mask such that the hole of the mask corresponds to a manufacturing portion of the metallic film; and
manufacturing the metallic film in the manufacturing portion of the metallic film through the hole of the mask.
The invention also provides a planar lightwave circuit having a metallic film in another aspect.
This planar lightwave circuit has the waveguide construction of an arrayed waveguide grating, and this waveguide construction comprises:
one or more optical input waveguides arranged side by side;
a first slab waveguide connected to the exit end of said optical input waveguides;
an arrayed waveguide connected to the exit end of said first slab waveguide, and consisting of a plurality of channel waveguides arranged side by side for transmitting light that has traveled through said first slab waveguide, said channel waveguides having different lengths with the difference preset;
a second slab waveguide connected to the exit end of the arrayed waveguide; and
a plurality of optical output waveguides arranged side by side and connected to the exit end of said second slab waveguide;
wherein a slab waveguide is divided into two by intersecting planes that intersect the route of the light traveling along the slab waveguide. The intersecting planes serve as dividing planes and divide a waveguide forming region into a first waveguide forming region that includes one portion of the divided slab waveguide and a second waveguide forming resion that includes the other portion of the divided slab waveguide. One or both of the first waveguide forming region and the second waveguide forming region are moved along the dividing planes by a position shifting member;
an end portion side of the position shifting member is fixed to at least the one of the first waveguide forming region and the second waveguide forming region through the metallic film; and
the metallic film is manufactured by the manufacturing method of the metallic film mentioned above.